Apparatus for controlling the discharge of a capacitor

ABSTRACT

A flash tube triggering capacitor and triggering transformer primary winding are connected in series across a power supply resistor to charge the capacitor. A bypass capacitor is connected in series with the terminals of a hot shoe across the resistor, and the terminals of a PC connector are also connected across the resistor. The completion of an electrical path between either the hot shoe terminals or the PC terminals discharges the triggering capacitor into the primary winding to fire a flash tube.

United States Patent Wallace [111 3,761,767 Sept. 25, 1973 Inventor:

APPARATUS FOR CONTROLLING THE DISCHARGE OF A CAPACITOR Robert H. Wallace, Littleton, Colo.

Assignee: Honeywell Inc., Minneapolis, Minn.

Filed: Dec. 28, 1970 Appl. No.1 101,779

US. Cl. 315/241 P, 315/239, 315/240, 315/241 R Int. Cl. 1105b 37/00 Field of Search 315/239, 241 R, 241 P, 315/240 References Cited UNITED STATES PATENTS 5/1961 Ludloff 315/241 P 9/1967 Neureuter 315/241 R X Primary Examiner-Roy Lake Assistant Examiner-Lawrence J. Dahl AttorneyArthur H. Swanson, Lockwood D. Burton and George E. Bodenstein [57] ABSTRACT A flash tube triggering capacitor and triggering transformer primary winding are connected in series across a power supply resistor to charge the capacitor. A bypass capacitor is connected in series with the terminals of a hot shoe across the resistor, and the terminals of a PC connector are also connected across the resistor. The completion of an electrical path between either the hot shoe terminals or the PC terminals discharges the triggering capacitor into the primary winding to fire a flash tube.

8 Claims, 1 Drawing Figure PATENTEI] SEP2519T5 INVENTOR. ROBERT H. WALLACE AGENT APPARATUS FOR CONTROLLING THE DISCHARGE OF A CAPACITOR BACKGROUND OF THE INVENTION The present invention relates generally to apparatus for actuating an electrical circuit upon the selective completion of either of two electrical paths, or upon the completion of one of these paths notwithstanding the concurrent existance of the other of the paths. Specifically, the invention relates to such apparatus wherein a charged capacitor is discharged into a load device upon the completion of an electrical path between the terminals of either one or the other of two pairs of terminals, or upon the completion of a path between the terminals of one of the pairs of terminals notwithstanding the concurrent presence of an already completed path between the terminals of the other of the pairs of terminals.

Apparatus is known in which the selective completion of an electrical path between one or another pair of terminals produces an electrical effect, such as the discharge of a charged capacitor into a load device. One example of such apparatus is the known photographic electronic flash unit which is provided with one pair of flash tube triggering or firing terminals in the form of the so-called PC connector, and with a second pair of flash tube firing terminals in the form of the socalled hot shoe. The completion of a path between either of these pairs of terminals, as is produced by the closing of camera shutter contacts connected between the terminals of that pair, causes the triggering capacitor of the triggering or firing circuit of the unit to be discharged into the associated triggering transformer and to fire the associated flash tube. It is necessary to provide such a unit with these two different forms of triggering or firing terminals in order to permit the unit to be used with, and to be fired by, both the type of camera in which the shutter contacts are connected to the terminals of a camera PC connector with which the terminals of the unit PC connector are designed to mate, and the type of camera in which the shutter contacts are connected to the terminals of a so-called camera hot accessory clip with which the terminals of the hotshoe of the unit are designed to mate when the unit is mounted and carried on the camera by means of this clip.

When a flash unit of the foregoing type is mounted by means of its hot shoe on the type of camera wherein the accessory clip is not provided with terminals, but is' merely a single metallic element, an electrical path is continuously completed between the hot shoe terminals. In other words, the hot shoe terminals are continuously short-circuited in this situation. In order to prevent this path from continuously short-circuiting the firing circuit of the unit and thus taking the control of the firing away from the PC terminals of the unit, such known units have been provided with one or another of several different means for allowing the PC terminals to control the firing notwithstanding the concurrent short-circuiting of the hot shoe terminals by a terminalless accessory clip. These means have included manually or automatically operated switches for effecting the disconnection of the hot shoe terminals from the firing circuit of the unit when the PC connector is to be used, and arrangements which require the PC connector to be plugged back into the unit in order that the hot shoe terminals will be connected to the unit firing circuit. Another of such means has included two separate triggering capacitor circuits in the firing circuit of the unit, one for the hot shoe terminals and one for the PC terminals, each circuit including a separate triggering capacitor and charging resistor therefor. In each case, however, such means have unduly added to the size, complexity, and cost of the flash devices employing these means.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved form of capacitor discharging apparatus of the type last described which is simpler, less costly, and more compact than the known forms of such apparatus as described herein. A specific object of the invention is to provide such improved apparatus which does not require any switching devices or any manually operated means for controlling the connection of one of two pairs of terminals to a capacitor discharging circuit, and does not require the use of separate charged capacitors or circuits and charging resistors therefor for each pair of controlling terminals. A more specific object of the invention is to provide such improved capacitor discharging apparatus in photographic electronic flash apparatus which does not require any switching devices or any manually operated means for controlling the connection of the hot shoe terminals to the flash tube firing circuit of the apparatus, or any second, duplicate triggering capacitor or circuit and charging resistor therefor.

In accomplishing the foregoing and other desirable objects, the improved apparatus provided in accordance with, and embodying, the present invention includes the connection of a bypass capacitor in series with a first pair of terminals, such as the hot shoe terminals of photographic electronic flash apparatus, which are connected between circuit points of the apparatus. These points are ones between which the completion of an electrical path causes a charged capacitor, such as a triggering capacitor, to discharge into a load device, such as a triggering transformer. These points may be connected directly across the series combination of the charged capacitor and the load device. Upon the completion of a path between the terminals of said first pair of terminals, a path is completed only temporarily between said points which causes the charged capacitor to discharge into the load device. The completion of a path between a second pair of terminals, such as PC connector terminals, which are also connected between said points, also causes the charged capacitor to discharge into the load device, even though there may already be the aforementioned path between the terminals of said first pair of terminals. A resistor is connected across the bypass capacitor to discharge the lat- 'ter in the absence of a path between said first pair of terminals.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention may be had from the following detailed description when read in connection with the accompanying drawing, wherein the single figure is a schematic circuit diagram of photographic electronic flash apparatus embodying capacitor discharging means according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The flash apparatus or unit illustrated in the drawing figure is one in which the flash tube of the unit is fired upon the completion of an electrically conductive or electrical path or connection, herein referred to as a path, between either the terminals of a hot shoe of the unit, or the terminals of a PC connector of the unit. Further, the completion of a path between said PC terminals fires the flash tube notwithstanding the concurrent presence of an already completed path between the hot shoe terminals,

To the end of providing such operation, the illustrated unit includes a flash tube 1 having main electrodes 2 and 3 which are connected, respectively, to supply conductors 4 and 5. The tube 1 also has a triggering electrode 6. The conductors 4 and 5 are connected across the usual flash storage capacitor 7, and to respective supply terminals 8 and 9. The latter connect the capacitor 7 to the usual capacitor charging means, not shown, which may well be of the type disclosed in the Schmidt et al. U. S. Pat. No. 3,310,723. Voltage dividing resistors 10 and 11 are connected in series between the conductors 4 and 5, and have a common junction 12.

The firing means for the tube 1 include a triggering capacitor 13 which is connected in series with the primary winding 14 of a triggering transformer 15 between a conductor 16, which is connected to the junction 12, and the conductor 5. The transformer 15 also has a secondary winding 17 which is connected between the triggering electrode 6 and the conductor 5. A first terminal 18 of a hot shoe 19 is connected in series with a bypass capacitor 20 to the conductor 16, while a second terminal 21 of the hot shoe 19 is connected to the conductor 5. A resistor 22 is connected in parallel with the capacitor 20. A first terminal 23 of a PC connector 24 is connected to the conductor 16, while a second terminal 25 of the connector 24 is connected to the conductor 5. Although the connector 24 is shown and described herein as being of the PC type, it is noted that the connector 24 could as well be of any of the many other types of shutter contact connectors which are used in the photographic field.

In the manner described in the aforementioned Schmidt et al. patent, the storage capacitor 7 is normally maintained in a charged state by the aforementioned capacitor charging means, whereby a suitably high voltage is normally maintained between the conductors 4 and 5. By virtue of the connection of the triggering capacitor 13 and the winding 14 in series between the conductors l6 and 5, and hence across the resistor 11, the capacitor 13 also is normally maintained in a charged state. Therefore, the completion of a path between the conductors 16 and 5 effectively connects the capacitor 13 across the winding 14, and causes the capacitor 13 to discharge into the winding 14. This in turn fires the tube 1, in the manner described in said Schmidt et al patent.

The tube 1 then continues to conduct until, due to this conduction, the charge on the capacitor 7, and hence the voltage between the conductors 4 and 5, drop sufficiently to cause the tube 1 to become extinguished. Thereafter, the capacitors 7 and 13 recharge to be ready for the next completion of a path between the conductors 16 and 5.

It is seen, therefore, that the conductors 16 and 5 constitute a pair of circuit points between which the completion of apath causes the charged capacitor 13 to discharge into the winding 14 to tire the flash tube 1. It is seen also that the hot shoe terminals 18 and 21 and the capacitor 20 are connected in a first series circuit between the conductors 16 and 5, while the PC terminals 23 and 25 are connected in a second series circuit between the conductors 16 and 5.

The ways in which a path may be completed between the conductors 16 and 5 to fire-the tube 1 will now be described. When the illustrated flash unit is to be used with and tired by a camera, not shown, of the type provided with a hot accessory clipthat is, a flash unit mounting clip having terminals connected to the camera shutter contacts the usual procedure is to mount the unit onto the camera by engaging the hot shoe 19 with the accessory clip. This causes the camera shutter contacts to be connected between the hot shoe terminals 18 and 21. When a photograph is to be taken by the camera, the shutter thereof is actuated, which causes the shutter contacts to close and to complete a path between the terminals 18 and 21. Since the bypass capacitor 20 doe not have a charge at this time, the completion of the path between the terminals 18 and 21 effectively completes a path between the conductors 16 and 5. As noted above, such a path causes the capacitor 13 to discharge into the winding 14, thereby firing the tube 1.

Since the camera shutter contacts usually stay closed only momentarily, the capacitor 20 usually acquires only a small charge under the foregoing conditons. When the camera shutter contacts open, any charge which has accumulated on the capacitor 20 is disipated by the resistor 22. As soon as the capacitors 7. and 113 become charged once more following the termination of the conduction of the tube 1, the unit is ready to be tired again by the next closure of the shutter contacts and completion of the path between the terminals 18 and 21.

When the illustrated flash unit is to be fired by means of the PC connector 24 instead of by the hot shoe 19,

the connector 24 is connected to the camera shutter contacts so that the latter are connected between the terminals 23 and 25. This may be done by means of the usual shutter cord, not shown. This use of the PC connector 24 is required when the associated camera is not provided with a hot accessory clip, or when it is desired, for one or another reason, to support the flash unit in a manner other than by engaging the hot shoe 19 with an accessory clip.

Whena photograph is to be taken under the conditions just described, the camera shutter is actuated, which causes the shutter contacts to close momentarily and to complete a path between the PC terminals 23 and 25. This in turn completes a path between the conductors 16 and 5, thereby causing the capacitor 13 to discharge into the winding 14 and to fire the tube 1. As soon as the capacitors 7 and 13 become recharged following the termination of the conduction of the tube 1, the unit is ready to be fired again by the next closure of the shutter contacts and completion of the path between the'terminals 23 and 25.

It is often desired to mount the illustrated flash unit on a camera by engaging the hot shoe 19 with an accessory clip on the camera even though this clip is not a hot clip, but is merely a suitably-shaped piece'of metal without any shutter contact or other terminals. Under these conditions, the PC connector 24 must be used to connect the camera shutter contacts to the flash unit.

As noted previously herein, however, this practice causes the hot shoe terminals to be continuously shortcircuited as long as the unit remains mounted on the camera. Specifically, the engagement of the hot shoe 19 with such a short-circuiting accessory clip causes a path to be completed between the terminals 18 and 21 which is maintained throughout the period in which the unit remains mounted on the camera. Were it not for the presence of the novel construction according to the present invention, this continuously completed path between the terminals 18 and 21 would result in the completion ofa path between the conductors 16 and 5, and across the PC terminals 23 and 25, throughout said period, during which the terminals 23 and 25 would have no control of the firing of the tube 1, and the latter would be caused to fire repeatedly in an uncontrolled manner.

The novel construction of the illustrated device prevents such undesirable action, however. When the hot shoe 19 is placed in engagement with a short-circuiting accessory clip, a path is completed between the terminals 18 and 21, and, for the time being, between the conductors l6 and 5. This causes the tube 1 to fire once, in the same manner as occurs upon the closure of the shutter contacts when the hot shoe 19 is in engagement with a hot accessory clip. ln the present case, however, the continued completion of the path between the terminals 18 and 21 causes the capacitor to become charged, since this capacitor now remains connected across the resistor 11. When the capacitor 20 becomes charged to the voltage across the resistor 11, the path between the conductors 16 and 5 effectively disappears. Thus, the completion of the path between the terminals 18 and 21 for an extended period only temporarily completes a path between the conductors 16 and 5. Accordingly, the continued presence of the path between the terminals 18 and 21, due to the presence of the short-circuiting accessory clip, does not cause the flash tube 1 to be repeatedly fired in an uncontrolled manner, but allows the terminals of the PC connector 24 to control the firing of the flash tube 1 as before. Therefore, each subsequent completion of a path between the PC terminals 23 and simultaneously completes a path between the conductors 16 and 5 and tires the flash tube as before, notwithstanding the concurrent presence of the path already completed between the hot shoe terminals 18 and 21 by the short-circuiting accessory clip.

When the hot shoe 19 is subsequently disengaged from the short circuiting accessory clip, the capacitor 20 is suitably discharged by the resistor 22. Accordingly, the device is then returned to the condition wherein the completion of a path between either the hot shoe terminals 18 and 21 on the PC terminals 23 and 25 completes a path between the conductors 16 and 5 and causes the flash tube 1 to fire.

In summary, it is seen that the described apparatus according to the present invention fulfills the objects set forth hereinbefore by employing a bypass capacitor in connection with a hot shoe and a PC connector in a relatively simple flash tube firing circuit which permits the terminals of the PC connector to control the firing of the flash tube even when the hot shoe terminals are short-circuited by a camera accessory clip. Moreover,

said described apparatus provides the foregoing operation without the use of any switching devices, any manually operated means, or any duplicated triggering capacitors or capacitor charging resistors.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for discharging a charged capacitor into a load device comprising a first capacitor connected in series with a load device to a source of capacitor charging voltage, and

means connected across the series combination of said first capacitor and said load device, said means including first and second circuit points between which the completion of an electrical path causes said first capacitor to discharge into said load device,

first and second terminals forming a first pair of terminals,

third and fourth terminals forming a second pair of terminals,

a second capacitor,

conductors connecting said first and second terminals and said second capacitor in a first series circuit between said points tocause said second capacitor to temporarily complete an electrical path between said points to effect the discharge of said first capacitor into said load device once upon each sustained as well as temporary connection of electrically conducting means between said first and second terminals, and

conductors directly connecting said third and fourth terminals to a second series circuit between said points to complete an electrical path between said points to effect the discharge of said first capacitor into said load device once upon each connection of electrically conducting means between said third and fourth terminals notwithstanding the concurrent presence of electrically conductng means already connected between said first and second terminals.

2. Apparatus as specified in claim .1, wherein said first series circuit is connected to said source of voltage to cause said second capacitor to become charged upon the sustained connection of electrically conducting means between said first and second terminals.

3. Apparatus as specified in claim 2, wherein a resistor is connected directly across said second capacitor to discharge the latter in the absence of the connection of electrically conducting means between said first and second terminals.

4. Apparatus as specified in claim 1, wherein said first capacitor and said load device are connected in a series circuit between first and second conductors connected across said source of voltage, and whereinsaid points are connected to said first and second conducfirst and second conductors connected across said first resistor, and wherein said points are connected to said first and second conductors, respectively.

8. Apparatus as specified in claim 7, wherein there is included a flash tube having electrodes connected across said storage capacitor, and wherein said triggering transformer includes a secondary winding arranged in firing relationship with said tube. 

1. Apparatus for discharging a charged capacitor into a load device comprising a first capacitor connected in series with a load device to a source of capacitor charging voltage, and means connected across the series combination of said first capacitor and said load device, said means including first and second circuit points between which the completion of an electrical path causes said first capacitor to discharge into said load device, first and second terminals forming a first pair of terminals, third and fourth terminals forming a second pair of terminals, a second capacitor, conductors connecting said first and second terminals and said second capacitor in a first series circuit between said points to cause said second capacitor to temporarily complete an electrical path between said points to effect the discharge of said first capacitor into said load device once upon each sustained as well as temporary connection of electrically conducting means between said first and second terminals, and conductors directly connecting said third and fourth terminals to a second series circuit between said points to complete an electrical path between said points to effect the discharge of said first capacitor into said load device once upon each connection of electrically conducting means between said third and fourth terminals notwithstanding the concurrent presence of electrically conductng means already connected between said first and second terminals.
 2. Apparatus as specified in claim 1, wherein said first series circuit is connected to said source of voltage to cause said second capacitor to become charged upon the sustained connection of electricallY conducting means between said first and second terminals.
 3. Apparatus as specified in claim 2, wherein a resistor is connected directly across said second capacitor to discharge the latter in the absence of the connection of electrically conducting means between said first and second terminals.
 4. Apparatus as specified in claim 1, wherein said first capacitor and said load device are connected in a series circuit between first and second conductors connected across said source of voltage, and wherein said points are connected to said first and second conductors, respectively.
 5. Apparatus as specified in claim 4, wherein said source of voltage is a first resistor which is connected in series with a second resistor across a storage capacitor.
 6. Apparatus as specified in claim 1, wherein said first capacitor is the triggering capacitor of a photographic electronic flash apparatus having a hot shoe connector and a PC connector arranged for connection to camera shutter contacts, wherein said load device is the primary winding of a flash tube triggering transformer, wherein said first and second terminals are terminals of said hot shoe connector, and wherein said third and fourth terminals are terminals of said PC connector.
 7. Apparatus as specified in claim 6, wherein said source of voltage is a first resistor which is connected in series with a second resistor across a flash storage capacitor, wherein said triggering capacitor and said primary winding are connected in a series circuit between first and second conductors connected across said first resistor, and wherein said points are connected to said first and second conductors, respectively.
 8. Apparatus as specified in claim 7, wherein there is included a flash tube having electrodes connected across said storage capacitor, and wherein said triggering transformer includes a secondary winding arranged in firing relationship with said tube. 